This invention relates to a process for producing purified cyclopentane from a feedstream containing cyclopentene and, optionally, neo-hexane. In a preferred embodiment, the invention relates to a process wherein a cyclopentene containing fraction and a neohexane containing fraction are separated from a hydrocarbon stream, the cyclopentene containing fraction further containing other chemical constituents. The cyclopentene containing fraction is subjected to hydrotreatment. Purified cyclopentane is separated from the hydrotreated stream.
Cyclopentane with a purity greater than 85% is a desirable product for solvents and polyurethane foaming agents. In addition, such cyclopentene may be used as a replacement for fluorocarbon refrigerants.
Typically, cyclopentane is recovered by fractionating natural gasoline at concentrations as low as 1.6 weight percent cyclopentane. It is difficult to process high purity cyclopentane from this process, however, since the contaminant neo-hexane has a boiling point very close to cyclopentane. While the boiling point of cyclopentene is about 111xc2x0 F., the boiling point of cyclopentane is approximately 120.7xc2x0 F. The boiling point of neo-hexane is approximately 121.5xc2x0 F. Thus, it is difficult to separate cyclopentane and neo-hexane efficiently. In fact, a practical maximum concentration of only 80 weight percent is possible from such fractionation processes. Further, such processes are both energy and capital intensive.
Cyclopentane can also be produced by backcracking dicyclopentadiene (DCPD) to cyclopentadiene. Cyclopentadiene is then hydrotreated to cyclopentane. This procedure, however, requires a backcracking reactor, a hydrotreater, and a post-fractionation unit. In addition, backcracking DCPD and converting it to cyclopentane has several negative factors. First, the backcracking reaction is highly endothermic, thereby requiring a fired heater. Second, low quality by-product DCPD streams have high value in the resin market. Thus, it is cost inefficient to use the DCPD as a feedstream. Third, hydrotreating cyclopentadiene requires large amounts of hydrogen at high capital costs.
A process for producing cyclopentane of high purity is therefore desired which avoids the problems of the prior art.
A process for producing cyclopentane from by-product streams containing cyclopentene consists of distilling the cyclopentene from the feedstream and then hydrotreating the cyclopentene-containing fraction to cyclopentane. A second distillation step may be employed to remove the hydrocarbons which are lighter than cyclopentane. In a preferred embodiment, the process consists of preparation of a purified cyclopentane stream from an impure cyclopentene containing fraction wherein the impure cyclopentene containing fraction is subjected to hydrotreatment.
The feedstream may be a by-product stream, such as one containing piperylene resins, or one from a delayed coking reactor as well as a stream from coal liquefication. In a preferred embodiment, the feedstream is obtained by steam cracking of olefins.
The process of the invention offers several advantages over the prior art. First, it permits the efficient removal of cyclopentene from a feedstream containing neo-hexane, also known as 2,2-dimethylbutane, since there is a 10xc2x0 temperature difference between cyclopentene and, when present, neo-hexane. Second, the process permits conventional distillation equipment and conditions to be used. Third, the hydrotreatment of the cyclopentene containing fraction to cyclopentane uses a minimum amount of hydrogen. Lastly, the final distillation step permits the removal of cyclopentane from the remaining contaminants, such as linear and branched olefins, which have a lower boiling point than cyclopentane.